HID: wiimote: fix FF deadlock

The input core has an internal spinlock that is acquired during event
injection via input_event() and friends but also held during FF callbacks.
That means, there is no way to share a lock between event-injection and FF
handling. Unfortunately, this is what is required for wiimote state
tracking and what we do with state.lock and input->lock.

This deadlock can be triggered when using continuous data reporting and FF
on a wiimote device at the same time. I takes me at least 30m of
stress-testing to trigger it but users reported considerably shorter
times (http://bpaste.net/show/132504/) when using some gaming-console
emulators.

The real problem is that we have two copies of internal state, one in the
wiimote objects and the other in the input device. As the input-lock is
not supposed to be accessed from outside of input-core, we have no other
chance than offloading FF handling into a worker. This actually works
pretty nice and also allows to implictly merge fast rumble changes into a
single request.

Due to the 3-layered workers (rumble+queue+l2cap) this might reduce FF
responsiveness. Initial tests were fine so lets fix the race first and if
it turns out to be too slow we can always handle FF out-of-band and skip
the queue-worker.

Cc: <stable@vger.kernel.org> # 3.11+
Reported-by: Thomas Schneider
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

2 files changed, 32 insertions, 12 deletions

diff --git a/drivers/hid/hid-wiimote-modules.c b/drivers/hid/hid-wiimote-modules.c
index 2e7d644dba18..71adf9e60b13 100644
--- a/drivers/hid/hid-wiimote-modules.c
+++ b/drivers/hid/hid-wiimote-modules.c
@@ -119,12 +119,22 @@ static const struct wiimod_ops wiimod_keys = {
  * the rumble motor, this flag shouldn't be set.
  */
 
+/* used by wiimod_rumble and wiipro_rumble */
+static void wiimod_rumble_worker(struct work_struct *work)
+{
+        struct wiimote_data *wdata = container_of(work, struct wiimote_data,
+                                                  rumble_worker);
+
+        spin_lock_irq(&wdata->state.lock);
+        wiiproto_req_rumble(wdata, wdata->state.cache_rumble);
+        spin_unlock_irq(&wdata->state.lock);
+}
+
 static int wiimod_rumble_play(struct input_dev *dev, void *data,
                               struct ff_effect *eff)
 {
         struct wiimote_data *wdata = input_get_drvdata(dev);
         __u8 value;
-        unsigned long flags;
 
         /*
          * The wiimote supports only a single rumble motor so if any magnitude
@@ -137,9 +147,10 @@ static int wiimod_rumble_play(struct input_dev *dev, void *data,
         else
                 value = 0;
 
-        spin_lock_irqsave(&wdata->state.lock, flags);
-        wiiproto_req_rumble(wdata, value);
-        spin_unlock_irqrestore(&wdata->state.lock, flags);
+        /* Locking state.lock here might deadlock with input_event() calls.
+         * schedule_work acts as barrier. Merging multiple changes is fine. */
+        wdata->state.cache_rumble = value;
+        schedule_work(&wdata->rumble_worker);
 
         return 0;
 }
@@ -147,6 +158,8 @@ static int wiimod_rumble_play(struct input_dev *dev, void *data,
 static int wiimod_rumble_probe(const struct wiimod_ops *ops,
                                struct wiimote_data *wdata)
 {
+        INIT_WORK(&wdata->rumble_worker, wiimod_rumble_worker);
+
         set_bit(FF_RUMBLE, wdata->input->ffbit);
         if (input_ff_create_memless(wdata->input, NULL, wiimod_rumble_play))
                 return -ENOMEM;
@@ -159,6 +172,8 @@ static void wiimod_rumble_remove(const struct wiimod_ops *ops,
 {
         unsigned long flags;
 
+        cancel_work_sync(&wdata->rumble_worker);
+
         spin_lock_irqsave(&wdata->state.lock, flags);
         wiiproto_req_rumble(wdata, 0);
         spin_unlock_irqrestore(&wdata->state.lock, flags);
@@ -1731,7 +1746,6 @@ static int wiimod_pro_play(struct input_dev *dev, void *data,
 {
         struct wiimote_data *wdata = input_get_drvdata(dev);
         __u8 value;
-        unsigned long flags;
 
         /*
          * The wiimote supports only a single rumble motor so if any magnitude
@@ -1744,9 +1758,10 @@ static int wiimod_pro_play(struct input_dev *dev, void *data,
         else
                 value = 0;
 
-        spin_lock_irqsave(&wdata->state.lock, flags);
-        wiiproto_req_rumble(wdata, value);
-        spin_unlock_irqrestore(&wdata->state.lock, flags);
+        /* Locking state.lock here might deadlock with input_event() calls.
+         * schedule_work acts as barrier. Merging multiple changes is fine. */
+        wdata->state.cache_rumble = value;
+        schedule_work(&wdata->rumble_worker);
 
         return 0;
 }
@@ -1756,6 +1771,8 @@ static int wiimod_pro_probe(const struct wiimod_ops *ops,
 {
         int ret, i;
 
+        INIT_WORK(&wdata->rumble_worker, wiimod_rumble_worker);
+
         wdata->extension.input = input_allocate_device();
         if (!wdata->extension.input)
                 return -ENOMEM;
@@ -1817,12 +1834,13 @@ static void wiimod_pro_remove(const struct wiimod_ops *ops,
         if (!wdata->extension.input)
                 return;
 
+        input_unregister_device(wdata->extension.input);
+        wdata->extension.input = NULL;
+        cancel_work_sync(&wdata->rumble_worker);
+
         spin_lock_irqsave(&wdata->state.lock, flags);
         wiiproto_req_rumble(wdata, 0);
         spin_unlock_irqrestore(&wdata->state.lock, flags);
-
-        input_unregister_device(wdata->extension.input);
-        wdata->extension.input = NULL;
 }
 
 static const struct wiimod_ops wiimod_pro = {
diff --git a/drivers/hid/hid-wiimote.h b/drivers/hid/hid-wiimote.h
index f1474f372c0b..75db0c400037 100644
--- a/drivers/hid/hid-wiimote.h
+++ b/drivers/hid/hid-wiimote.h
@@ -133,13 +133,15 @@ struct wiimote_state {
         __u8 *cmd_read_buf;
         __u8 cmd_read_size;
 
-        /* calibration data */
+        /* calibration/cache data */
         __u16 calib_bboard[4][3];
+        __u8 cache_rumble;
 };
 
 struct wiimote_data {
         struct hid_device *hdev;
         struct input_dev *input;
+        struct work_struct rumble_worker;
         struct led_classdev *leds[4];
         struct input_dev *accel;
         struct input_dev *ir;